You’ve got love simple hacks like this one that give you access to a tool you don’t otherwise have or can’t afford. Adam Fleisch modified a $5 Harbor Freight airgun and a .77 fitting and used a soda bottle to create a super-cheap but what appears to be effective sandblasting gun.
The only really futzy part was cutting in the 1/2″ feed trough in the blower tube using a grinding wheel. But that can be easily done. Then it’s just a matter of drilling a hole through the soda bottle, filling it was blast medium, and firing away.
I’m not sure how robust this solution is (e.g. it looks like you have to hold the bottle upright as you blast), but for a one-time project or for periodic blasting work, I’d imagine this would work just fine. It certainly wouldn’t cost a lot, in money or time, to find out.
Here is Fleisch’s full Instructable.
Update: We’ve gotten a few comments about the health and safety risks of using crushed glass blast medium, uncontained, in an open shop environment. Before trying this blaster gun, especially if you are new to blasting, do your research into proper use, use the most benign medium, wear proper safety gear, and follow relevant safety instructions.